1. Field of the Invention
The invention is in the general field of air purification and sterilization devices. In particular, the invention is more specifically in the area of ultraviolet (UV) mediated air purification and sterilization devices, in particular photocatalytic oxidation devices.
2. Description of the Related Art
The interior air in dwellings and vehicles is often unsatisfactory or unpleasant due to the presence of airborne contaminants such as dust particles, allergens (e.g. pollen, pet dander, dust mite feces, mold spores), as well as living bacteria or bacterial spores, living molds or mold spores, viruses, and volatile organic compounds (VOC). As a result, there has been a significant amount of interest in developing improved devices and methods for removing these various contaminants.
Although filters, such as high efficiency particulate air (HEPA) filters can remove some of the particulate contaminants, many HEPA filters still allow smaller particles, such as particles of 0.3 micrometers in diameter or less, to pass through the filter. Thus the industry has turned to secondary systems, such as photocatalytic oxidation (PCO) systems. These systems typically generate hydroxyl radicals and super-oxide ions by exposing semiconductor particles to UV light rays, usually in the presence of at least trace amounts of moisture from the atmosphere. These hydroxyl radicals and super-oxide ions in turn react with the airborne contaminants and can oxidize the contaminants, ideally breaking the contaminants down into simpler molecules such as carbon dioxide and water, and at least neutralizing the biological capability (i.e. sterilizing) any living airborne spores, bacteria, moulds, or viruses. Additionally, the allergenic effect of non-living allergens can also be reduced or eliminated.
As a result, a number of different types of photocatalytic UV air purifiers/sterilizers are presently on the market. Although effective, these devices are often difficult to maintain. The UV light sources, electronics, and photocatalytic surfaces used in these devices often have a limited lifetime (often a year or less). As a result, service and replacement of these various limited-lifetime components can place a burden on unskilled users. Air purifiers must be disassembled, UV lighting sources extracted from catalytic elements and their support electronics, the defective part removed, a new part added, and then the entire unit must be reassembled, often with the use of tools. As a result, due to the inconvenience of servicing, many of these purifiers/sterilizers often run using out-dated components running at substandard levels of efficiency.
Another problem with prior art devices is that many photocatalytic UV air purifiers force the air through complex catalytic fabric or catalytic mesh structures that can act to limit air flow. As a result, even though the actual effectiveness of the photocatalytic UV air purifier on any given pass of the air through the device may be high, the net effectiveness of the air purifier may still be inadequate. This is because due to the low flow rates, only a small amount of the air in the room or vehicle may be processed in any given period of time.
Unfortunately, in most air purifier uses, the air is recirculated. That is, the devices are set up so that “dirty” air from the room is processed into “clean” air, and this clean air is then placed back into the room with the remaining dirty air. Thus due to mixing, the effectiveness of the clean air is thus reduced by the large amount of “dirty” air. Thus low air flow also causes many prior art photocatalytic UV air purifiers/sterilizers to operate at substandard efficiency as well.
As a result, further improvements in the design of photocatalytic UV air purifiers are desirable.